The exhaust gas of internal combustion engines contains various amounts of unburned hydrocarbons, carbon monoxide and nitrogen oxides. Emission of these materials to the atmosphere is undesirable. The problem is more acute in urban areas having a high concentration of motor vehicles.
During recent years, researchers have investigated extensively means of reducing exhaust emissions. This research has been quite fruitful. As a result, present-day automobiles emit only a fraction of undesirable materials compared to those of less than a decade ago.
Despite the tremendous advances that have been made, further improvements are desirable. Federal standards continue to require reduction of emissions. A major obstacle in achieving further reduction in exhaust emissions is the fact that up to eighty percent of hydrocarbon emissions over the Federal Testing Procedure cycle are generated during the first 1-2 minutes of operation of a vehicle engine following a cold start.
There are several factors that contribute to excess hydrocarbon emissions at low engine temperatures. One of the primary functions is that the emission system catalyst does not achieve its optimum operating temperature until 1-2 minutes after a cold start and thus it is incapable of oxidizing all of the unburned fuel. This problem is exacerbated as a result of significant over-fueling because of the difficulty in vaporizing a sufficient fraction of the fuel to achieve stable combustion below 30.degree. Celsius.
In the past, attempts have been made to eliminate the need for a warm-up period by operating the engine on liquid petroleum gas, or other secondary fuels, during the warm-up period and then switching to gasoline after an operating temperature is obtained. The concept was used, for example, on tractors and other machinery. These devices had a separate fuel tank that was filled with a second type of fuel different from the fuel in the main tank. The fuel supply was then selected with a manually operated petcock valve.
Due to the difficulties and impracticalities of using two separate fuels and two fuel source systems, other systems were developed which separated a single fuel into two components, one being more volatile than the other one. Systems of this type are shown, for example, in U.S. Pat. Nos. 5,357,908, 3,783,841, and 3,794,000.
The systems disclosed in these references, however, still had limitations, including the initial use of the primary fuel remaining in the fuel line at start-up, undesirable delays in starting the engine, the need for additional pressurization and heating systems, and/or the use of complicated and expensive components. Therefore, there is a need for a less complicated and less expensive system that separates fuel into various components, provides an improved air-fuel mixture at engine start-up, and, as a result, reduces hydrocarbon emissions.